Exceptional Mechanical Properties and Heat Resistance of Photocurable Bismaleimide Ink for 3D Printing

Photosensitive resins used in three-dimensional (3D) printing are characterized by high forming precision and fast processing speed; however, they often possess poor mechanical properties and heat resistance. In this study, we report a photocurable bismaleimide ink with excellent comprehensive performance for stereolithography (SLA) 3D printing. First, the main chain of bismaleimide with an amino group (BDM) was synthesized, and then, the glycidyl methacrylate was grafted to the amino group to obtain the bismaleimide oligomer with an unsaturated double bond. The oligomers were combined with reaction diluents and photo-initiators to form photocurable inks that can be used for SLA 3D printing. The viscosity and curing behavior of the inks were studied, and the mechanical properties and heat resistance were tested. The tensile strength of 3D-printed samples based on BDM inks could reach 72.6 MPa (166% of that of commercial inks), glass transition temperature could reach 155 °C (205% of that of commercial inks), and energy storage modulus was 3625 MPa at 35 °C (327% of that of commercial inks). The maximum values of T_-5%, T_-50%, and T_max of the 3D samples printed by BDM inks reached 351.5, 449.6, and 451.9 °C, respectively. These photocured BDM inks can be used to produce complex structural components and models with excellent mechanical and thermal properties, such as car parts, building models, and pipes.     

Water-Soluble Copper Ink for the Inkjet Fabrication of Flexible Electronic Components

The aim of this work is preparation and investigation of copper conductive paths by printing with a different type of functional ink. The solutions based on copper-containing complex compounds were used as inks instead of dispersions of metal nanoparticles. Thermal characteristics of synthesized precursors were studied by thermogravimetry in an argon atmosphere. Based on the comparison of decomposition temperature, the dimethylamine complex of copper formate was found to be more suitable precursor for the formation of copper layers. Structure and performance of this compound was studied in detail by X-ray diffraction, test of wettability, printing on flexible substrate, and electrical measurements.     

3D Bioprinting of Biosynthetic Nanocellulose-Filled GelMA Inks Highly Reliable for Soft Tissue-Oriented Constructs

Bioink-formulations based on gelatin methacrylate combined with oxidized cellulose nanofibrils are employed in the present study. The parallel investigation of the printing performance, morphological, swelling, and biological properties of the newly developed hydrogels was performed, with inks prepared using methacrylamide-modified gelatins of fish or bovine origin. Scaffolds with versatile and well-defined internal structure and high shape fidelity were successfully printed due to the high viscosity and shear-thinning behavior of formulated inks and then photo-crosslinked. The biocompatibility of 3D-scaffolds was surveyed using human adipose stem cells (hASCs) and high viability and proliferation rates were obtained when in contact with the biomaterial. Furthermore, bioprinting tests were performed with hASCs embedded in the developed formulations. The results demonstrated that the designed inks are a versatile toolkit for 3D bioprinting and further show the benefits of using fish-derived gelatin for biofabrication.     

Mapping the Volume Transfer of Graphene-Based Inks with the Gravure Printing Process: Influence of Rheology and Printing Parameters

It is a common practice to add rheology modifiers to functional inks, such as graphene inks, to optimize the rheological properties so that they can be printed with a certain printing technique. This practice may lead to inks formulations with poorer electrical, optical, and mechanical performance upon its application, which are of paramount importance in printed electronics. In this study, we demonstrate for three different commercial graphene-based inks that it is possible to control the amount of ink transferred to the flat surface by tweaking printing parameters, such as the velocity and the length scale of the gravure cell, without modifying the rheology of the ink. Finally, the results are summarized in printing maps based on dimensionless numbers, namely, the capillary and Reynolds numbers.     

Design of a Waterborne Polyurethane–Urea Ink for Direct Ink Writing 3D Printing

In this work, polycaprolactone–polyethylene glycol (PCL–PEG) based waterborne polyurethane–urea (WBPUU) inks have been developed for an extrusion-based 3D printing technology. The WBPUU, synthesized from an optimized ratio of hydrophobic polycaprolactone diol and hydrophilic polyethylene glycol (0.2:0.8) in the soft segment, is able to form a physical gel at low solid contents. WBPUU inks with different solid contents have been synthesized. The rheology of the prepared systems was studied and the WBPUUs were subsequently used in the printing of different pieces to demonstrate the relationship between their rheological properties and their printing viability, establishing an optimal window of compositions for the developed WBPUU based inks. The results showed that the increase in solid content results in more structured inks, presenting a higher storage modulus as well as lower tan δ values, allowing for the improvement of the ink’s shape fidelity. However, an increase in solid content also leads to an increase in the yield point and viscosity, leading to printability limitations. From among all printable systems, the WBPUU with a solid content of 32 wt% is proposed to be the more suitable ink for a successful printing performance, presenting both adequate printability and good shape fidelity, which leads to the realization of a recognizable and accurate 3D construct and an understanding of its relationship with rheological parameters.     

Suitability of Paper-Based Substrates for Printed Electronics

Flexible plastic substrates are widely used in printed electronics; however, they cause major climate impacts and pose sustainability challenges. In recent years, paper-based electronics has been studied to increase the recyclability and sustainability of printed electronics. The aim of this paper is to analyze the printability and performance of metal conductor layers on different paper-based substrates using both flexography and screen printing and to compare the achieved performance with that of plastic foils. In addition, the re-pulpability potential of the used paper-based substrates is evaluated. As compared to the common polyethylene terephthalate (PET) substrate, the layer conductivity on paper-based substrates was found to be improved with both the printing methods without having a large influence on the detail rendering. This means that a certain surface roughness and porosity is needed for the improved ink transfer and optimum ink behavior on the surface of the substrate. In the case of uncoated paper-based substrates, the conductivity and print quality decreased by preventing the formation of the proper and intimate ink-substrate contact during the ink transfer. Finally, the re-pulpability trials together with layer quality analysis detected very good, coated substrate candidates for paper-based printed electronics competing with or even outperforming the print quality on the reference PET foil.     

Development and Characterizations of Novel Aqueous-Based Ceramic Inks for Inkjet Printing

Stable rheological properties of ceramic ink are a key requirement for inkjet printing (IJP), which should be satisfied in terms of the Reynolds and Weber numbers. In this paper, the reverse microemulsion was introduced for the synthesis of monodispersed nanosized ceramic powders, and the average size was less than 100 nm. A comparison of two different dispersants, i.e., polyacrylic ammonium (PAANH₄) and polyacrylic aid (PAA), revealed that the former exerted a good dispersion effect on the ceramic ink. The sedimentation ratio, zeta potential, surface tension, viscosity, and density of the inks were measured, and the Reynolds and Weber numbers, as well as Z value, were calculated. A stable, homogeneous, and high solid loading (20 wt%) ceramic ink could be achieved after aging for a period of 72 h. Finally, the ceramic inks showed the desired printable property in the inkjet printing process. Combining inkjet printing technology with a sintering process, Ni-Mn-O films have the potential to monitor temperature and humidity parameters for intelligent wearable devices.     

Experimental Study on Metal Parts under Variable 3D Printing and Sintering Orientations Using Bronze/PLA Hybrid Filament Coupled with Fused Filament Fabrication

Producing metal parts from Fused Filament Fabrication (FFF) 3D printing coupled with a metal/polymer hybrid filament, considering the advantages of high-performance and low cost, has generated considerable research interest recently. This paper addresses the studied relationship between variable printing/sintering directions and the properties of the sintered metal parts. It was shown that the printing directions played a significant role in determining the properties of final products, such as shrinkage, tensile stress, and porosity. The shrinkage in the layer direction because of anisotropic behavior is more minor than in the other dimensions. The microstructural analysis indicated that the printing directions had influenced the form and position of porosity on the produced metal parts. Most porosities occurred on the surfaces printed parallel to the printing bed. Furthermore, the sintering orientations had no possible benefits for dimension shrinkage, weight shrinkage, density, and porosity position of produced metal parts. However, the sintering direction “upright” resulted in parting lines inside the sintered tensile samples and made them fragile. The best printing-sintering combination was “on-edge-flat”.     

Microstructural and Process Characterization of Conductive Traces Printed from Ag Particulate Inks

Conductive inks are key enablers for the use of printing techniques in the fabrication of electronic systems. Focus on the understanding of aspects controlling the electrical performance of conductive ink is paramount. A comparison was made between microparticle Ag inks and an Ag nanoparticle ink. The microstructures resulting from thermal cure processes were characterized morphologically and also in terms of their effect on the resistivity of printed traces. For microparticle inks, the variability of resistivity measurements between samples as defined by coefficient of variation (CV) was greater than 0.1 when the resistivity was 10 to 50 times that of bulk Ag. When the resistivity was lower (~1.4 times that of bulk Ag) the CV of sample sets was less than 0.1. In the case of the nanoparticle ink, resistivity was found to decrease by a factor ranging from 1.2 to 1.5 after doubling the amount of layers printed prior to curing though it was expected to remain the same. Increasing the amount of layers printed also enhanced the sintering process.     

Sustainable Additive Manufacturing: Mechanical Response of Polyethylene Terephthalate Glycol over Multiple Recycling Processes

The continuous demand for thermoplastic polymers in a great variety of applications, combined with an urgent need to minimize the quantity of waste for a balanced energy-from-waste strategy, has led to increasing scientific interest in developing new recycling processes for plastic products. Glycol-modified polyethylene terephthalate (PETG) is known to have some enhanced properties as compared to polyethylene terephthalate (PET) homopolymer; this has recently attracted the interest from the fused filament fabrication (FFF) three-dimensional (3D) printing community. PET has shown a reduced ability for repeated recycling through traditional processes. Herein, we demonstrate the potential for using recycled PETG in consecutive 3D printing manufacturing processes. Distributed recycling additive manufacturing (DRAM)-oriented equipment was chosen in order to test the mechanical and thermal response of PETG material in continuous recycling processes. Tensile, flexure, impact strength, and Vickers micro-hardness tests were carried out for six (6) cycles of recycling. Finally, Raman spectroscopy as well as thermal and morphological analyses via scanning electron microscopy (SEM) fractography were carried out. In general, the results revealed a minor knockdown effect on the mechanical properties as well as the thermal properties of PETG following the process proposed herein, even after six rounds of recycling.     

Reinforced 3D Composite Structures of γ-, α-Al2O3 with Carbon Nanotubes and Reduced GO Ribbons Printed from Boehmite Gels

The ability of boehmite to form printable inks has sparked interest in the manufacturing of 3D alumina (Al₂O₃) and composite structures by enabling direct ink writing methods while avoiding the use of printing additives. These materials may exhibit high porosity due to the printing and sintering procedures, depending on the intended application. The 3D-printed porous composite structures of γ-Al₂O₃ and α-Al₂O₃ containing 2 wt.% of carbon nanotubes or reduced graphene oxide ribbons were fabricated from boehmite gels, followed by different heat treatments. The reinforcing effect of these carbon nanostructures was evidenced by compression tests carried out on the different alumina structures. A maximum relative increase of 50% in compressive strength was achieved for the γ-Al₂O₃ composite structure reinforced with reduced graphene oxide ribbons, which was also accompanied by an increase in the specific surface area.     

How the Thermomechanical Processing Can Modify the High Strain Rate Mechanical Response of a Microalloyed Steel

The effects of thermomechanical processing (TMP) on the mechanical response of microalloyed steels subjected to dynamic loading conditions were examined. The deformation conditions in the thermomechanical laboratory rolling processes were selected on the basis of dilatometric tests. It allowed (with a constant value of total deformation) us to obtain microstructures with different compositions and morphology of the particular components. Several samples characterized by a particularly complex and unexpected representation of the obtained microstructures were selected for further research. Plastometric tests, i.e., compression and tensile tests, were performed under quasi-static loading with digital image correlation (DIC) analysis, and under dynamic loading on the Split Hopkinson Pressure Bar (SHPB) apparatus with strain rates of 1400 and 2000 s⁻¹. Samples deformed in such conditions were subjected to microstructural analysis and hardness measurements. It has been observed that the use of various combinations of TMP parameters can result in the formation of specific microstructures, which in turn are the source of an attractive mechanical response under dynamic loading conditions. This opens up new possible areas of application for such popular structural materials which are microalloyed steels.     

Alumina and Zirconia-Reinforced Polyamide PA-12 Composites for Biomedical Additive Manufacturing

This work aimed to prepare a composite with a polyamide (PA) matrix and surface-modified ZrO₂ or Al₂O₃ to be used as ceramic fillers (CFs). Those composites contained 30 wt.% ceramic powder to 70 wt.% polymer. Possible applications for this type of composite include bioengineering applications especially in the fields of dental prosthetics and orthopaedics. The ceramic fillers were subjected to chemical surface modification with Piranha Solution and suspension in 10 M sodium hydroxide and Si₃N₄ to achieve the highest possible surface development and to introduce additional functional groups. This was to improve the bonding between the CFs and the polymer matrix. Both CFs were examined for particle size distribution (PSD), functional groups (FTIR), chemical composition (XPS), phase composition (XRD), and morphology and chemical composition (SEM/EDS). Filaments were created from the powders prepared in this way and were then used for 3D FDM printing. Samples were subjected to mechanical tests (tensility, hardness) and soaking tests in a high-pressure autoclave in artificial saliva for 14, 21, and 29 days.     

Effects of Disulfiram on Positron Emission Tomography and Neuropsychological Studies in Severe Chronic Alcoholism

Disulfiram is an aldehyde dehydrogenase inhibitor that is widely used as an adjunctive agent in the treatment of patients with severe chronic alcoholism. Recent positron emission tomography (PET) studies of local cerebral metabolic rates for glucose (ICMRglc) and benzodiazepine receptor binding in alcoholic patients have shown regional cerebral abnormalities; however, some of the patients were studied while receiving disulfiram, which could influence the biochemical processes under investigation. In a retrospective investigation, we examined the influence of disulfiram administration on the results of PET studies of ICMRglc and benzodiazepine receptor binding and neuropsychological tests of cognition and executive function in patients with severe chronic alcoholism. [¹⁸F]Fluorodeoxyglucose was used to measure ICMRglc in 48 male patients, including 11 receiving and 37 not receiving disulfiram in therapeutic doses. [¹¹C]Flumazenil was used to measure benzodiazepine receptor binding in 17 male patients, including 3 receiving and 14 not receiving disulfiram. All patients studied with FMZ were also examined with fluorodeoxyglucose. PET studies of ICMRglc revealed significantly decreased global values in the patients receiving disulfiram compared with those not receiving disulfiram. PET studies of benzodiazepine receptor binding revealed decreased flumazenil influx and distribution volume in patients receiving disulfiram. The neuropsychological tests demonstrated no differences between the two groups of subjects. The findings suggest that disulfiram may influence the results of PET studies of glucose metabolism and benzodiazepine receptor binding.     

Copper Nanoparticles for Printed Electronics: Routes Towards Achieving Oxidation Stability

In the past few years, the synthesis of Cu nanoparticles has attracted much attention because of its huge potential for replacing expensive nano silver inks utilized in conductive printing. A major problem in utilizing these copper nanoparticles is their inherent tendency to oxidize in ambient conditions. Recently, there have been several reports presenting various approaches which demonstrate that copper nanoparticles can resist oxidation under ambient conditions, if they are coated by a proper protective layer. This layer may consist of an organic polymer, alkene chains, amorphous carbon or graphenes, or inorganic materials such as silica, or an inert metal. Such coated copper nanoparticles enable achieving high conductivities by direct printing of conductive patterns. These approaches open new possibilities in printed electronics, for example by using copper based inkjet inks to form various devices such as solar cells, Radio Frequency Identification (RFID) tags, and electroluminescence devices. This paper provides a review on the synthesis of copper nanoparticles, mainly by wet chemistry routes, and their utilization in printed electronics.     

Micro-to-Nanometer Scale Patterning of Perovskite Inks via Controlled Self-Assemblies

In the past decade, perovskite materials have gained intensive interest due to their remarkable material properties in optoelectronics and photodetectors. This review highlights recent advances in micro-to-nanometer scale patterning of perovskite inks, placing an undue emphasis on recently developed approaches to harness spatially ordered and crystallographically oriented structures with unprecedented regularity via controlled self-assemblies, including blade coating, inkjet printing, and nanoimprinting. Patterning of the perovskite elements at the micro- or nanometer scale might be a key parameter for their integration in a real system. Nowadays, unconventional approaches based on irreversible solution evaporation hold an important position in the structuring and integration of perovskite materials. Herein, easier type patterning techniques based on evaporations of polymer solutions and the coffee ring effect are systematically reviewed. The recent progress in the potential applications of the patterned perovskite inks is also introduced.     

The Effect of Harsh Environmental Conditions on Concrete Plastic Shrinkage Cracks: Case Study Saudi Arabia

Due to climate change and population expansion, concrete structures are progressively being subjected to more extreme environments. As the environment affects plastic shrinkage directly, there is a need to understand the effect of environmental changes on plastic shrinkage cracking. This paper examines the plastic shrinkage crack development parametrically at low, mid, and high drying environmental conditions, corresponding to different environments in three Saudi cities. The effects of water-cement ratios and quantities of recycled tire steel fibers (RTSF) in concrete are also investigated. The different environmental conditions for the plastic shrinkage tests were simulated in a specially designed chamber as per ASTM C1579, 2006. A digital image processing (DIP) technique was used to monitor crack initiation and development. Through the use of the crack reduction ratio (CRR), it was found that 30 kg/m³ of RTSF can control plastic shrinkage cracks at low and mid conditions. For the more extreme (high) conditions, the use of 40 kg/m³ of RTSF fiber was sufficient to completely eliminate surface plastic shrinkage cracks. This work can help develop more sustainable concrete structures in a wider set of environmental conditions and help mitigate the impact of climate change on concrete infrastructure.     

An Overview on the Rheology,Mechanical Properties,Durability, 3D Printing,and Microstructural Performance of Nanomaterials in Cementitious Composites

The most active research area is nanotechnology in cementitious composites, which has a wide range of applications and has achieved popularity over the last three decades. Nanoparticles (NPs) have emerged as possible materials to be used in the field of civil engineering. Previous research has concentrated on evaluating the effect of different NPs in cementitious materials to alter material characteristics. In order to provide a broad understanding of how nanomaterials (NMs) can be used, this paper critically evaluates previous research on the influence of rheology, mechanical properties, durability, 3D printing, and microstructural performance on cementitious materials. The flow properties of fresh cementitious composites can be measured using rheology and slump. Mechanical properties such as compressive, flexural, and split tensile strength reveal hardened properties. The necessary tests for determining a NM’s durability in concrete are shrinkage, pore structure and porosity, and permeability. The advent of modern 3D printing technologies is suitable for structural printing, such as contour crafting and binder jetting. Three-dimensional (3D) printing has opened up new avenues for the building and construction industry to become more digital. Regardless of the material science, a range of problems must be tackled, including developing smart cementitious composites suitable for 3D structural printing. According to the scanning electron microscopy results, the addition of NMs to cementitious materials results in a denser and improved microstructure with more hydration products. This paper provides valuable information and details about the rheology, mechanical properties, durability, 3D printing, and microstructural performance of cementitious materials with NMs and encourages further research.     

Large-Scale Preparation of Silver Nanowire-Based Flexible Transparent Film Heaters by Slot-Die Coating

Highly flexible silver nanowire-based transparent conductive films (AgNWs TCFs) were large-scale fabricated by slot-die coating AgNWs inks on a flexible polyethylene terephthalate (PET) substrate, and further fabricated into a transparent film heater. Appropriate flow rate, coating speed, and AgNWs concentration allow the construction of the 15 cm × 15 cm AgNW TCFs with a sheet resistance (R_s) of less than 20 Ω/sq, a transmittance (T) at 550 nm higher than 95%, and a haze less than 3.5%. The resultant AgNW TCFs heater possesses high uniformity and superior mechanical stability and can reach a Joule heating temperature of 104 °C with a voltage of 12 V. The slot-die coating method has great potential for large-scale production of AgNW based film heaters promisingly used in window defrost and deicer systems.     

Influence of Nanoclay on the Thermo-Mechanical Properties of Silicone Pressure-Sensitive Adhesives

This research was carried on newly obtained innovative materials—self-adhesive one-sided tapes based on silicone pressure-sensitive adhesives. In order to obtain tapes, the stable adhesive composition was subjected to physical modification by incorporating into it various amounts of selected silicon fillers. The produced pressure-sensitive adhesives were tested for viscosity and thermogravimetric analysis, as well as the manufactured tapes; i.e., peel adhesion, tack, cohesion at room and elevated temperature, SAFT test (shear adhesive failure temperature), and shrinkage. The prepared self-adhesive tapes retained their self-adhesive properties at a level close to the initial level while increasing the thermal resistance by 70–75 °C, reaching the level of 220–225 °C. The new self-adhesive materials have application potential and can be used as a material for special applications in the field of electrical engineering and heavy industry.